X-ray crystallography is being used by a greater number of researchers at the University of Colorado at Boulder to study the structures of macromolecules. While this has created a favorable local environment for structural biology it has also increased the demand for an X-ray data collection system initially set up for a few "designated" crystallography labs. This application requests funds to purchase a Rigaku/MSC R-AXIS IV++ X-ray area detector together with a Blue Max-Flux Confocal optical system. The new detector and optics system will be used with an existing RUH-3R X-ray generator and a Rigaku/MSC Xtreme cooling device as part of our X-ray core facility housed in the basement of the Cristol Chemistry Building. The new instrument will enhance the use of existing resources and greatly improve our in-house data collection capacity. The new equipment will benefit the research programs of five major users (Robert Batey, Thomas Cech, Lin Chen, Norman Pace and Marcelo Sousa) and a number of minor users between the departments of Chemistry and Biochemistry and Molecular, Cellular and Developmental Biology (MCDB). The titles of the research projects are listed below: Structural studies of RNA and RNA-protein complexes (Robert Batey) Structural studies of Ribozymes and Telomere Complexes (Group I introns and Pot I) (Thomas Cech) Structure and function of the NFAT and MEF2 complexes (Lin Chen) Structural studies of RNase P (Norman Pace) Structural studies of eukaryotic calcium signaling and bacterial antibiotic resistance (Marcelo Sousa) Structure-function studies of catalytic RNAs (Hammerhead Ribozyme) (Arthur Pardi) Structural biology and biochemistry of Telomeres (Cdc13) (Deborah Wuttke) Structural studies of the prokaryotic and eukaryotic chemotaxis pathways (Joseph Falke) Structure and mechanism at the chemical synapse (Michael Stowell)